A transceiver is used to transmit information in a communication system, e.g. a mobile radio system or a wire based communication system. The transceiver architecture for implementing broadband transmission standards, such as UMTS (Universal Mobile Telecommunications System), requires the generation of suitable clock signals for use in the respective standard. In a common communication system the clock signal is too high to be generated directly using a crystal oscillator. Therefore, oscillator circuitry is provided to generate the clock signal.
While transmission frequencies used in a communication system are becoming higher, the interference between the transmission signal and clock signals is getting more important. The interference may cause degradation in the quality of signal transmission. In consequence, increased demands are imposed on a spectral purity of the clock signals. In particular, the clock signal should have a minimum amount of phase noise (jitter).
As soon as clock signals at a higher frequency are required, a DLL (Delay-Locked Loop) circuit may be used to multiply the frequency of the crystal oscillator. A DLL circuit is a control loop in which an oscillator is stabilized by means of a reference frequency signal. The spectral purity of the clock generated in this manner is sufficient to supply a clock signal to digital blocks such as DSP (Digital Signal Processing) blocks and digital/analogue converters (DACs), for example. However, the quality of a clock signal generated in a DLL is insufficient in terms of the spectral purity required. It may not be used as a reference signal for a so-called phase-locked loop (PLL) to generate the transmission signal. For this and other reasons, there is a need for the present invention.